I. Field of the Invention
The present invention relates to communication systems and more particularly to a method of configuring a system so that multiple formats and protocols are supported.
II. Prior Art
In a computer network, a terminal, such as the widely used IBM 3270 display control unit, is used as an interface between a user and a host computing system. Terminals may be asynchronous, where characters are transmitted one at a time between the host computer and the terminal, or synchronous, where characters are stored up in a buffer until the entire group is assembled. Although asynchronous terminals are the most common and the least expensive, synchronous terminals, such as the IBM 3270, are more efficient.
Although the communications lines from the terminals can be attached directly to the host computer, it is more common to use a cluster controller or a communications controller between the host computer system and the terminals. A cluster controller often consists of a small computer whose sole job is to control the operation of a group, or cluster, of terminals. A communications controller, among many other things, performs many communication-related functions, thus freeing up the host computer for application-related work. An example of a cluster controller is the IBM 3174 establishment controller.
The communications lines attaching the controller and the various terminals can be, at least theoretically, comprised of most any type of communications medium. The most common, however, is two-conductor cabling, such as coaxial, twisted pair and twisted shielded pair cabling. The term "Coax" will be used for the remainder of this specification to represent any of these cabling types (or equivalent).
Data is transmitted over the Coax medium between the host computer, the controller and the terminals in accordance with standard formats and protocols (FAPs). The two communicating units, i.e., a controller and a terminal, must support the same FAP in order to properly communicate.
There are a number of existing FAPs used for communicating across the Coax medium. The various FAPS normally correspond to the different types of terminals which can connect to the host computer. Examples of two 3270-type terminals having specific Coax FAPs are control unit terminals (CUTs) and distributed function terminals (DFTs).
The different types of terminals perform different functions depending upon the user's needs. For instance, CUTs do not interpret the 3270 data stream themselves, nor can they execute functions independently of the controller. The controller interprets the data stream and executes functions for the CUT. But, if a user wishes to obtain local reliability, availability and serviceability (RAS), network management and configuration information directly from the controller to which the user is attached, a CUT is required.
DFTs, on the other hand, cannot obtain the local RAS, network management and configuration information directly from the controller as can a CUT. But, the DFT can interpret the data stream and execute functions independently of the controller.
Distributed function terminal extended (DFT-E) is an extension of the DFT and enables a device and a controller to support a DFT interface and a limited CUT interface on the same device/controller port simultaneously. Thus, a user having the DFT-E function can have CUT and DFT sessions simultaneously.
Another FAP for operating with the 3174 establishment controller, not specifically related to a particular 3270-type terminal, is 3174 Peer Communication. 3174 Peer Communication allows existing intelligent devices to form a star-wired LAN segment that is bridged to an IBM Token-Ring through the 3174 Establishment Controller. 3174 Peer Communication provides a way for intelligent devices to communicate peer-to-peer, increase connectivity options, retain host connectivity, and share resources, such as files, data bases, application programs, and printers.
Each of the described FAPs provides a user with unique functions unsupported by other FAPs. It is desirable for a device and a controller to be able to support multiple FAPs simultaneously on the same device/controller port. In this manner a user can have active connections via multiple FAPs simultaneously.
Presently, the DFT-E function enables a device and a controller to support CUT and DFT simultaneously. DFT-E does not, however, allow for the additional support of the 3174-Peer FAP. Likewise, DFT-E does not allow for the additional support of any other FAP which may, in the future, become desirable. Presently, there is no generic process for combining the support of multiple Coax FAPs.